Ambient noise from a sound system?

As long as the speakers aren’t facing the direction where the wedding is being held it should be alright. Well as long as the show isn’t to amped up like a rock show or something.

Sure they will hear it. The question is, will it be disruptive? Maybe you can work with them and not make noise during their vows or speeches. That would be the courteous thing to do.

Do a little experiment yourself. You’ll see that if things are quiet you can hear your system even if it is aimed away.

Think how would you like to be treated. Talk with them. They will appreciate your concern.

Is your event going to be as far away as feasible from the wedding?

This sounds like a disaster waiting for a place to happen. I have run sound for any number of events. The ambient sound (regardless of how you direct the speakers) will likely impact the wedding (particularly sound in the lower ranges—think bass and drums). I agree with @worriedguy that it would likely bode well for you to talk to the wedding folks. They may be able to turn up their music loud enough that they don’t hear you all, but that may not work for you (or people in their party who find their stuff too loud).

You will definitely be able to hear it. We went to a birthday party in the park and our setups were even further apart then you are describing. The other group set up their regular old boombox with speakers and blasted Norteno oompah music until we were forced to leave. I don’t think they thought their music was loud.

You should either try to work out a timed plan with the wedding group, or maybe move your setup to another park.